Hard tissue, such as natural bone, comprises collagen and inorganic calcium phosphate, particularly biological apatite. Bone contains about 60% to 75% by weight of biological apatite and tooth contains more than 98% by weight of biological apatite. Biological apatite is a naturally occurring calcium apatite-type material, which is formed in the body by precipitation from body fluids. Biological apatite has a structure, which is similar to pure carbonated apatite, but contains some substitute ions for the calcium, phosphate and carbonate ions. Synthetically produced precipitated hydroxyapatite is typically more similar to biological apatite than are the hydroxyapatite ceramics.
Collagen can be mineralized by calcium phosphate minerals by inducing the precipitation of calcium phosphate in a collagen slurry. Several patents have disclosed methods of preparation of mineralized collagen by precipitation of calcium phosphate.
For example, U.S. Pat. No. 5,320,844 discloses a mineralized collagen composite material produced by quickly adding a soluble calcium ion-containing solution and a phosphate ion-containing solution into a collagen slurry. The patent further discloses that the slurry is vigorously stirred while maintaining it at a basic pH to thereby induce the mineralization of the collagen. The mineralized collagen is disclosed as being recovered by solid-liquid separation and is then dried.